In a controller area network (CAN), which is a kind of in-vehicle communication network, a differential signal is transmitted through a bus consisting of a pair of signal lines by applying a voltage between the signal lines so that the bus can be in a dominant level. The signal lines of the bus are generally called the “CAN_High” and the “CAN_low”. When the bus is not in the dominant level, the signal lines are at the same potential so that the bus can be in a recessive level.
In such a communication network, when the bus changes between the recessive level and the dominant level, ringing (i.e., overshoot and undershoot) in a signal waveform occurs. For example, when the bus changes from the dominant level to the recessive level, undershoot may occur due to the energy of electric current stored in an inductance of the bus.
In a technique disclosed in US 2006/0066358 A1 corresponding to JP 2006-101430 A, when undershoot occurs, a freewheel diode connected between signal lines of a bus is turned on to reduce the undershoot.
The technique disclosed in US 2006/0066358 A1 has the following disadvantages. When the freewheel diode is a PN junction diode having an on-voltage of about 0.8V, the freewheel diode cannot be turned on unless the undershoot exceeds 0.8V. Since a Schottky diode has an on-voltage of about 0.3V, the Schottky diode may be used as the freewheel diode. However, the use of the Schottky diode as the freewheel diode results in an increase in leak current and a decrease in resistance to voltage breakdown.